Magnetron having internal conductive material coated area between anode terminals



14, 1965 G. J. CARLSON 3,223,883 MAGNETRON HAVING INTERNAL CONDUCTIVE MATERIAL COATED AREA BETWEEN ANODE TERMINALS Filed NOV. 50, 1962 INVENTORZ GERALD J. CARLSON /7 BY ATTOm United States Patent 3,223,883 MAGNETRON HAVING INTERNAL CONDUCTIVE MATERIAL COATED AREA BETWEEN ANODE TERMINALS Gerald J. Carlson, Schenectady, N.Y., assignor to General Electric Company, a corporation of New York Filed Nov. 30, 1962, Ser. No. 241,224 6 Claims. (Cl. SIS-39.51)

This invention relates to radio frequency apparatus and pertains more particularly to a new and improved voltage tunable magnetron, and to new and improved means for obtaining frequency tuning and bandwidth adjustments with such a device mounted in a resonant cavity circuit.

Voltage tunable magnetrons are often of the interdigital type, such, for example, as those disclosed and claimed in US. Patent No. 2,810,096 of P. H. Peters, Jr. et al. and US. Patent No. 2,930,933 of G. J. Griffin et al., both assigned to the same assignee as the present invention. Briefly, these devices include an envelope having sealed in the wall thereof a longitudinally-spaced pair of anode terminals which support internally of the envelope in mutually insulated relation interdigitallyarranged sets of anode segments. The anode segments define a central space in which is coaxially mounted a non-ernissive cathode which cooperates with the anode segments to define an annular interaction space. Longitudinally spaced from the non-emissive cathode are an emissive cathode and control means for directing electrons axially into the interaction space. A device of the just-described type is adapted for use in an oscillatory circuit. In such a circuit the interdigital anode segments of the device provide the required capacitance and the device can be mounted in a resonator cavity to provide the required inductance. In order to vary the operating center frequency or to adjust the operating bandwidth of such a circuit it is ordinarily necessary to vary the design dimensions of the tube or cavity circuit or to provide special electrical tuningcircuitry external of the apparatus or mechanical tuning means for altering the effective internal dimensions of the cavity circuit.

The present invention contemplates means effective for providing center frequency tuning and bandwidth adjustments of a voltage tunable magnetron involving the provision of a predeterminedly dimensioned metalized area on the internal surface of the tube insulator disposed between the anode terminals of the tube and predeterminedly angularly located relative to the R.F. output coupler of a cavity resonator having the tube mounted therein. This manner of center frequency tuning and obtaining bandwidth adjustments obviates the need for altering either the basic construction or dimensions of the tube or cavity and eliminates the need for special tuning circuitry and mechanical tuning means. Thus, it lends itself to the provision of different apparatus effective for operating at different locations of the R.F. spectrum with tubes and cavity circuits which are structurally essentially identical except for differences in the internal metalized areas provided in the tubes.

Accordingly, a primary object of the present invention is to provide a new and improved voltage tunable magnetron including new and improved means for varying the center operating frequency and effecting bandwidth adjustments of an oscillatory circuit incorporating such a magnetron.

Another object of the present invention is to provide new and improved means for effecting center frequency tuning and bandwidth adjustments of a voltage tunable magnetron circuit which does not require altering either the basic construction or dimensions of the elements comprising such circuitry.

Another object of the present invention is to provide new and improved means for effecting center frequency tuning and bandwidth adjustments of a voltage tunable magnetron cavity without the use of external electrical circuitry or mechanical tuning elements in the cavity.

Another object of the present invention is to provide new and improved means for effecting center frequency tuning and bandwidth adjustments of a voltage tunable magnetron circuit which enables the provision of a family of voltage tunable magnetron packages which are adapted for operating at different center frequencies and bandwidths but which can be basically structurally identical.

Still another object of the present invention is to provide new and improved means for effecting center frequency tuning and bandwidth adjustments of a voltage tunable magnetron circuit in a manner which substanially reduces manufacturing effort and costs and which involves the use of processing techniques which are standard and readily available in the electron tube art.

Further objects and advantages of this invention will become apparent as the following description proceeds and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

In carrying out the objects of this invention there is provided an interdigital voltage tunable magnetron having a pair of spaced anode terminals and a reentrant resonant cavity. The cavity has the opposed walls thereof apertured for receiving the opposite ends of the tube and for serving as coaxial electrical contacts adapted for making circumferential electrical contact with the anode terminals. Extending laterally from one side of the circuit is a coaxial R.F. output comprising an inductive coupling loop extending into the cavity and preferably the anode terminals for serving as the RF. output coupler. The anode terminals support interdigital anode segments in mutually-spaced relation in the magnetron envelope and are axially spaced and separated by an insulative wall section of the envelope. Provided on the internal surface of this wall section and conductively interconnecting the anode terminals is a metalized area of predetermined dimensions and predetermined angular position relative to the R.F. output coupler. This coating can be configured to introduce a predetermined inductance between the anode terminals. Alternatively, the coating can be adapted for introducing a predetermined capacitance between the anode terminals.

For a better understanding of the invention, reference may be had to the accompanying drawing in which:

FIGURE 1 is an enlarged sectional view of a voltage tunable magnetron tube constructed according to a feature of the invention;

FIGURE 2 is a greatly enlarged sectionalized side elevational view of R.F. apparatus incorporating the device of FIGURE 1;

FIGURE 3 is a partially broken away plan view of the apparatus of FIGURE 2;

FIGURE 4 is an enlarged perspective view illustrating the anode insulator incorporated in the device shown in FIGURES 13;

FIGURE 5 is a fragmentary illustration of a modified form of the invention; and

FIGURE 6 is a perspective illustration of the insulator in a modified form of the invention.

Referring to FIGURE 1, there is illustrated therein a voltage tunable magnetron generally designated 1. The magnetron 1 can be of the type disclosed and claimed in the above-noted patent of G. J. Griffin et al. Briefly, the magnetron 1 is constructed to include stacked alternate ceramic and metal elements. The ceramic elements generally include a plurality of cylindrical ceramic wall sections 2 and an apertured disk-like ceramic end cap 3.

The metal members are suitably brazed to or between opposed surfaces of the ceramic elements to complete a hermetically-sealed envelope and include a metal end cap 4 carrying a cylindrical non-emissive cathode 5 extending centrally in a cylindrical space defined by a plurality of anode segments generally designated 6. The anode segments 6 are arranged in a pair of interdigital sets, with each segment being carried by a washer-like anode contact ring or terminal 7. The terminals 7 are each sealed between a pair of the ceramic cylinders 2 and are thus mutually insulated. A filamentary emitter 8 is suitably mounted on the ceramic end cap with leads sealed therethrough and connected to a pair of buttonlike contact members 9 bonded to the outer surface of the ceramic end cap. A frusto-conical control electrode 10 is sealed between one of the ceramic insulators 2 and the ceramic end cap 3 and is positioned about the emitter 8. By means of a lead not shown and which extends also in a sealed manner through the ceramic end cap 3 an electrical connection is made between the control ring 10 and a third button-like contact member 11 bonded to the outer surface of the ceramic end cap.

The magnetron 1 is adapted for operating while axially aligned with a magnetic field provided, for example, by a magnet structure including opposed pole pieces designated N and S as in FIGURE 2. Additionally, the magnetron is adapted for operating with suitable direct current potentials applied to the various electrodes and supplied through the metal end cap 4 and the contact buttons 9 and 11 by means of D.C. leads generally designated 12 in FIGURE 2.

The radio frequency circuit of the apparatus illustrated includes the anode segments 6 and the anode terminals 7. Additionally, the circuit includes as an essential part thereof a resonant cavity generally designated 13. The cavity 13, as seen in FIGURE 3, can be circular and reentrant and can comprise a cup-like body having a cylindrical outer side wall 14, a reentrant bottom 15 which includes a cylindrical wall 16 and a transverse end wall 17. Additionally, the cavity includes a washer-like cover 18 held in place by a plurality of machine screws, for example. i

The bottom 17 is centrally apertured for receiving one end of the magnetron 1 and for affording a coaxial contact surface adapted for making circumferential electrical contact with one of the anode terminals 7. The cavity receives the opposite end of the magnetron and makes circumferential electrical contact with the other anode ring 7 through an annular retaining member 19 threaded in the cover 18 in a manner to engage the other anode terminal and hold the magnetron tightly in place in the cavity.

During operation of the magnetron strong magnetic fields are established between the anode terminals 7 in the cavity 13, and provided for transmitting radio frequency energy out of the cavity 12 is a coaxial coupler 20. The coaxial coupler 20 includes a tubular outer conductor 21 suitably mounted in the side wall 14 of the cavity and extending radially outwardly therefrom. An inner conductor 22 of the coupler 20 has an end portion extending radially inwardly and bent to define a generally J-shaped inductive loop 23 adapted for coupling R.F. energy from the cavity to a coaxial line connected to the coupler 20.

The loop 23 is flattened such as to define an energy intercepting section which is substantially wider than the cross-section of the portion of the inner conductor in the tubular section 21 of the coaxial coupler. Additionally, the inductive loop 23 extends sufiiciently inwardly to dispose the looped end portion between the anode terminals of the magnetron. Still further, the extreme inner end portion, or the portion which turns back on the main portion, of the flattened loop rests on and engages electrically the planar surface of one of the anode terminals 7. Additionally, the length of the J-shaped portion and the substantial width thereof provides for maximum linking or inductive relation with the magnetic flux present in the cavity during the operation of the magnetron. In order to hold the loop 23 in place in the desired position between the anode terminals 7 there are provided insulative support members 24 and 25. Electrically speaking, this arrangement afiords a very tight coupling between the load represented by the coaxial coupler 20 and the magnetron 1 with the desired elfect of lowering the Q of the circuit. With the Q thusly lowered the circuit is adapted for more efficient operation over a substantially wide range of operating frequencies of the magnetron. The just-described R.F. circuit apparatus including the reentrant resonator cavity and tight RF. coupling arrangement does not constitute part of the present invention but is disclosed and claimed in US. Patent No. 2,973,455 of R. H. Marlowe, entitled, Radio Frequency Apparatus, issued February 28, 1961, and assigned to the same assignee as the present invention.

The present invention is effective for providing center frequency tuning and bandwidth adjustments in the above described type of apparatus without necessitating any dimensional variations of either the magnetron or circuit element or the use of additional apparatus. More specifically, and as seen in FIGURES 1-4, the present invention involves the provision of a metalized area, or conductive coating, 26 extending across the internal surface 27 of the anode insulator 2 of the magnetron 1 or, in other words, that one of the ceramic insulators 2 which constitutes an insulative wall section and is positioned between the anode terminals 7. The metalized area 26 conductively interconnects the anode terminals internally of the envelope and can be applied to the ceramic 2 in accordance with any of the previously disclosed well-known metalizing techniques. By way of example, the metalized area 26 can be applied by first masking off the area not to be metalized for thusly leaving exposed the area to be metalized. The exposed area can then be coated with the low-temperature metalizing compound disclosed and claimed in US. Patent 3,023,492 of R. H. Bristow, entitled, Metalized Ceramic Member and Composition and Method for Manufacturing Same, issued March 6, 1962 and assigned to the same assignee as the present invention. After the ceramic is thusly coated it is sintered at about 1250 C. in a non-oxidizing atmosphere. Subsequently the metalized ceramic is copper plated and the copper adheres to only the metalized area. The ceramic is then ready for assembly in the tube structure 1 illustrated in FIGURE 1.

As explained above and as best seen in FIGURES 3 and 4, the conductive coating 26 extends across the width of the anode insulator 2 in order to enable it to interconnect conductively the anode terminals sealed thereto. However, it is limited to a predetermined circumferential area of the inner surface of the anode insulator. The tube center frequency and bandwidth are both functions of a circumferential extension or length of the coating 26. More specifically, the center frequency increases as the circumferential length of the conductive coating 26 is increased and, conversely, the bandwidth decreases as the circumferential length of the conductive coating is increased.

As noted above, the conductive coating 26 electrically interconnects, or electrically short-circuits, the two anode elements and thusly the coating behaves similar to a tuned cavity. By being located internally of the tube envelope and extending within the above-mentioned range of circumferential extension, the coating 26 has the effect of closing down, or making smaller, the mentioned tuned cavity and thus particularly adapts the apparatus for a high center frequency. If the coating 26 Were located on the outer surface of the ceramic 2 it would be more remotely located relative to the anode segments and thus not adapted for affording the same high center frequency. Additionally, the presently disclosed structure is adapted for increasing the oscillating frequency of the magnetron without decreasing the tube size. This is a substantial advantage in view of the fact that decreases in tube size invariably involve increases in manufacturing problems. Further, the internal location of the coating 26 serves to protect it from damage and exposure to the external atmosphere and adverse effects that can result therefrom, whereby the tuning and adjustment effect are rendered more reliable and the effective operating life of the magnetron is enhanced. For example, R.F. apparatus incorporating magnetrons tuned according to the present invention have been found to be reliable over extended tube lives of more than 1000 hours. Still further, the coating 26 on the inner surface of the anode insulator affords the desired center frequency tuning and bandwidth adjustment effects without requiring modifications of any of the other tube or circuit elements. That is, a given apparatus design can be adapted for a different operating center frequency or bandwidth adjustment simply by coating the internal surface of the anode insulator a predetermined amount. None of the tube elements, such as anode segments, or the RP. cavity, need be affected as by machining differently-shaped or dimensioned elements or cavities. This enables the provision of a family of devices adapted for different predetermined cen ter frequencies and bandwidth characteristics but differing structurally only by the circumferential lengths of the conductive coatings 26. Additionally, it has been found that the coating 26 is adapted for reducing the effects of modes other than the desired 71' mode.

While the above-discussed internal conductive coating 26 has both center frequency tuning and bandwith adjustment effects regardless of the circumferential dimension thereof, it has been found that particularly desirable center frequency tuning and bandwidth adjustments are obtainable when the coating 26 extends over an area having a circumferential length within the range of from approximately 120 to 190.

The following table demonstrates the center frequencies and bandwidths of tubes having no coating 26 and others having conductive coatings 26 of 120 and 190.

In accordance with another feature of the present invention the magnetron tube 1 is rotatably mounted in the cavity 13. This adapts the apparatus for adjustable center frequency tuning by predeterminedly rotatively positioning, or orienting, the conductive coating 26 in the tube 1 relative to a position diametrically opposite the RF output coupler 23. That is, the tube 1 is positioned in the cavity 13 so as to locate the coating 26 generally diametrically opposite the output coupler and in this position the mentioned center frequency is determined by the circumferential length of the coating 26. However, this center frequency can be adjusted further by moving the coating 26 angularly relative to the center position, or the position generally 180 from the R.F. coupling loop 23. This enables a Vernier adjustment of the center frequency determined by the circumferential length of the coating 26. After such an adjustment the retaining member 19 can be tightened for holding the tube in the predetermined adjusted position.

While the conductive coating 26 has been shown and described as a straight conductive interconnection between the anode terminals, it is to be understood from the foregoing that the coating 26 can, if desired, be in other forms, such for example, as a serpentine form designated 30 in FIGURE 5 for introducing a predetermined inductance between the anode terminals. Also, if desired, the coating 26 can be split horizontally to provide a ca- 6 pacity gap of the type designated 31 in FIGURE 6 and affording a predetermined capacitance between the anode terminals which can be relied upon for lowering the center frequency.

It is to be understood from the foregoing that the present invention is not limited to the use of a resonant cavity as the RF. circuit structure. Other resonant RF. circuit structures, such as resonant line-over-ground plane circuits, are equally employable.

While specific embodiments of the invention have been shown and described it is not desired that the invention be limited to the particular forms shown and described, and it is intended by the appended claims to cover all modifications within the spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A magnetron comprising an annular insulator, an anode circuit including a pair of axially spaced annular terminals sealed to opposite ends of said insulator and a plurality of segments supported in cylindrical array from said terminals in mutually-spaced relation with alternate segments connected to one said terminals and the remaining segments connected to the other of said terminals, a conductive coating on a portion only of the inner surface only of said insulator effective for controlling the center frequency of said magnetron, a nonemissive electrode supported concentrically within the space defined by said segments for providing an interaction space, an electron emissive electrode displaced axially relative to said non-emissive electrode, and means for controllably directing electrons axially into said interaction space.

2. A magnetron comprising an annular ceramic insulator, an anode circuiting including a pair of axially spaced annular terminals sealed to opposite ends of said insulator and a plurality of segments supported in cylindrical array from said terminals in mutually spaced relation with alternate segments connected to one of said terminals and the remaining segments connected to the other of said terminals, a metallic coating extending a predetermined circumferential distance on the internal surface only of said insulator and effectively interconnecting said anode terminals to lower the center frequency and increase the bandwidth of said magnetron, a non-emissive electrode supported concentrically within the space defined by said segments for providing an interaction space, an electron emissive electrode displaced axially relative to said nonemissive electrode, and means for controllably directing electrons axially into said interaction space.

3. A magnetron according to claim 2, wherein said metallic coating comprises a coextensive metallized area extending between approximately and on the inner surface of said insulator.

4. A magnetron according to claim 1, wherein said coating defines a capacity gap effective for introducing a predetermined capacitance between said terminals.

5. In combination, an interdigital magnetron comprising an evacuated envelope having a longitudinally spaced pair of anode terminals sealed through the wall of said envelope and separated by an insulative section of said wall, an anode circuit comprising a plurality of segments supported in said envelope in cylindrical array with alternate segments connected to one anode terminal and the remaining segments connected to the other anode terminal, a single conductive coating on a portion only of the inner surface of said insulative section, a resonant circuit having said magnetron mounted therein with each said terminals electrically contacting an opposite side of said resonant circuit, R.F. output means coupled to said resonant circuit, and said magnetron being positioned in said resonant circuit with said conductive coating disposed generally diametrically opposite the position of said output means.

6. In combination, an interdigital magnetron comprising an evacuated envelope having a longitudinally-spaced pair of anode terminals sealed through the wall of said envelope and separated by an insulative section of said wall, an anode circuit comprising a plurality of segments supported in said envelope in cylindrical array with alternate segments connected to one anode terminal and the remaining segments connected to the other anode terminal, a single area metallic coating extending circumferentially between approximately 120 and 190 on the inner surface of said insulator and electrically interconnecting said terminals, a resonant cavity having said magnetron mounted therein with each said terminal electrically contacting an opposite side of said cavity, a coaxial R.F. output coupler mounted in one side of said cavity and including an inductive coupling loop extending be- 8 tween said anode terminals, and said magnetron being rotatively positioned in said cavity with said conductive coating predeterminedly angularly positioned relative to a point diametrically opposite said coupling loop.

References Cited by the Examiner I UNITED STATES PATENTS 2,477,633 8/1949 Litton 3l5-39 2,973,455 2/1961 Marlowe 315-39 3,013,180 12/1961 Peters 31539.53 X 3,195,010 7/1965 Lock 31539.63 X

GEORGE N. WESTBY, Primary Examiner. 

1. A MAGNETRON COMPRISING AN ANNULAR INSULATOR, AN ANODE CIRCUIT INCUDING A PAIR OF AXIALLY SPACED ANNULAR TERMINALS SEALED TO OPPOSITE ENDS OF SAID INSULATOR AND A PLURALITY OF SEGMENTS SUPPORTED IN CYLINDRICAL ARRAY FROM SAID TERMINALS IN MUTUALLY-SPACED RELATION WITH ALTERNATE SEGMENTS CONNECTED TO ONE SAID TEMINALS AND THE REMAINING SEGMENTS CONNECTED TO THE OTHER OF SAID TERMINALS, A CONDUCTIVE COATING ON A PORTION ONLY OF THE INNER SURFACE ONLY OF SAID INSULATOR EFFECTIVE FOR CONTROLLING THE CENTER FREQUENCY OF SAID MAGNETRON, A NONEMISSIVE ELECTRODE SUPPORTED CONCENTRICALLY WITHIN THE SPACE DEFINED BY SAID SEGMENTS FOR PROVIDING AN INTERACTION SPACE, AN ELECTRON EMMISSIVE ELECTRODE DISPLACED AXIALLY RELATIVE TO SAID NON-EMISSIVE ELECTRODE, AND MEANS FOR CONTROLLABLY DIRECTING ELECTRONS AXIALLY INTO SAID INTERACTION SPACE. 